Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

16. Conjugated Systems

Stability of Conjugated Intermediates

Organic Chemistry

16. Conjugated Systems

Stability of Conjugated Intermediates

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Problem 54c

Textbook Question

Which of the following reactions would you expect to be faster/more favorable in each pair? Why?
(c)

Verified step by step guidance

Identify the functional groups in each reaction. The first reaction involves a ketone, while the second involves an aldehyde.

Recall that aldehydes are generally more reactive than ketones due to less steric hindrance and the electron-withdrawing effect of the carbonyl group being more pronounced.

Consider the role of the base in the reaction. The base will likely deprotonate the alpha hydrogen, leading to the formation of an enolate ion.

Compare the acidity of the alpha hydrogens in both compounds. The alpha hydrogen in the aldehyde is more acidic than in the ketone, making it easier to deprotonate.

Conclude that the reaction involving the aldehyde is expected to be faster/more favorable due to the higher reactivity and acidity of the alpha hydrogen compared to the ketone.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Aldol Condensation

Aldol condensation is a reaction where enolates, formed from aldehydes or ketones, react with carbonyl compounds to form β-hydroxy ketones or aldehydes. This reaction is base-catalyzed and involves the formation of a new carbon-carbon bond. Understanding the stability of the enolate ion and the electrophilicity of the carbonyl carbon is crucial for predicting the reaction's favorability.

Enolate Ion Formation

Enolate ions are formed when a base abstracts an alpha hydrogen from a carbonyl compound, resulting in a resonance-stabilized anion. The acidity of the alpha hydrogen and the strength of the base influence the formation of enolates. In the given reactions, the presence of a carbonyl group increases the acidity of the alpha hydrogen, making enolate formation more favorable in the top reaction.

Carbonyl Reactivity

Carbonyl compounds are highly reactive due to the polarization of the carbon-oxygen double bond, making the carbon electrophilic. This reactivity is crucial in reactions like aldol condensation, where the carbonyl carbon acts as an electrophile. The presence of the carbonyl group in the top reaction increases the electrophilicity, making the reaction more favorable compared to the bottom reaction, which lacks this group.

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